CVE-2026-3296: Everest Forms WordPress Plugin RCE Flaw

CVE-2026-3296 Overview

The Everest Forms plugin for WordPress contains a critical PHP Object Injection vulnerability affecting all versions up to and including 3.4.3. This insecure deserialization flaw occurs via the processing of untrusted input from form entry metadata, allowing unauthenticated attackers to inject malicious serialized PHP objects through any public form field.

The vulnerability stems from the plugin's use of PHP's native unserialize() function on stored entry meta values without specifying the allowed_classes parameter. This unsafe deserialization occurs in the html-admin-page-entries-view.php file when administrators view form entries. Attackers can craft malicious payloads that bypass sanitize_text_field() sanitization, as serialization control characters are not stripped, enabling stored payloads to persist in the wp_evf_entrymeta database table until triggered.

Critical Impact

Unauthenticated attackers can achieve remote code execution by injecting malicious PHP objects through public form submissions, which execute when administrators view form entries.

Affected Products

• Everest Forms WordPress Plugin versions up to and including 3.4.3
• WordPress installations running vulnerable Everest Forms versions
• Websites with publicly accessible Everest Forms forms

Discovery Timeline

• April 8, 2026 - CVE-2026-3296 published to NVD
• April 8, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3296

Vulnerability Analysis

This PHP Object Injection vulnerability represents a severe security risk due to its unauthenticated attack surface and stored payload nature. The vulnerability is classified under CWE-502 (Deserialization of Untrusted Data), a well-documented weakness that can lead to arbitrary code execution when proper input validation is not implemented.

The attack chain is particularly dangerous because it operates in two phases: first, an unauthenticated attacker submits a malicious serialized PHP object through any public Everest Forms form field. Second, the payload remains dormant in the database until an administrator triggers the vulnerability by viewing form entries. This stored nature means the attack can be deployed silently and executed at a later time when an admin performs routine entry review.

The sanitize_text_field() function, which is designed to clean user input, does not strip serialization control characters. This allows the serialized payload to remain intact when stored in the wp_evf_entrymeta database table, preserving the malicious object structure.

Root Cause

The root cause of CVE-2026-3296 is the unsafe use of PHP's unserialize() function in the html-admin-page-entries-view.php file at line 133. The code processes stored entry meta values without passing the allowed_classes parameter, which would restrict which classes can be instantiated during deserialization.

When unserialize() is called without class restrictions, any PHP class available in the application context can be instantiated with attacker-controlled properties. If a suitable "gadget chain" exists within WordPress core, the Everest Forms plugin, or any other installed plugin, attackers can leverage magic methods like __wakeup(), __destruct(), or __toString() to achieve code execution.

Attack Vector

The attack is network-based and requires no authentication or user interaction from the attacker's perspective. An attacker can exploit this vulnerability by:

1. Identifying a WordPress site running a vulnerable version of Everest Forms with a public form
2. Crafting a serialized PHP object payload containing a gadget chain available in the target environment
3. Submitting the payload through any form field that accepts text input
4. Waiting for an administrator to view the form entries, triggering the deserialization

The payload structure exploits the fact that WordPress's sanitize_text_field() does not strip serialization markers such as O: (object), a: (array), s: (string), and their associated length indicators. This allows the complete serialized object to be stored and later processed by the vulnerable unserialize() call.

For technical implementation details, refer to the vulnerable source code at line 133 and the core functions implementation.

Detection Methods for CVE-2026-3296

Indicators of Compromise

• Unusual serialized data patterns in form submissions containing O: object markers followed by class names
• Suspicious entries in the wp_evf_entrymeta database table containing serialized PHP objects
• Unexpected PHP errors or warnings related to class instantiation when viewing form entries
• Evidence of unauthorized file creation or modification following admin entry review

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block serialized PHP object patterns in form submissions
• Monitor WordPress admin activity logs for unusual behavior following form entry viewing
• Deploy file integrity monitoring on WordPress installations to detect unauthorized changes
• Review database contents for suspicious serialized data in the wp_evf_entrymeta table
• Utilize SentinelOne's behavioral AI to detect anomalous PHP process execution patterns

Monitoring Recommendations

• Enable detailed logging for WordPress admin actions, particularly form entry access
• Configure alerts for form submissions containing serialization control characters
• Monitor server-side PHP process spawning for unexpected child processes
• Implement database query logging to detect unusual patterns in entry metadata access

How to Mitigate CVE-2026-3296

Immediate Actions Required

• Update Everest Forms plugin to version 3.4.4 or later immediately
• Review recent form submissions for suspicious serialized data patterns
• Audit the wp_evf_entrymeta database table for potentially malicious entries
• Consider temporarily disabling public forms until the update is applied
• Implement WAF rules to block serialized PHP object patterns as an additional defense layer

Patch Information

The vulnerability has been addressed in Everest Forms version 3.4.4. The fix modifies the deserialization handling to prevent arbitrary class instantiation. Administrators should update through the WordPress plugin management interface or download the patched version directly from the WordPress plugin repository.

For detailed patch changes, review the plugin changeset between versions 3.4.3 and 3.4.4 and the readme.txt changes.

Additional security intelligence is available from the Wordfence vulnerability report.

Workarounds

• If immediate patching is not possible, disable all public Everest Forms until the update can be applied
• Implement input validation at the web server level to reject form submissions containing serialized PHP object patterns
• Restrict admin access to trusted IP addresses to limit the trigger surface
• Consider using a Web Application Firewall with rules specifically targeting PHP object injection payloads

# Configuration example - Apache mod_security rule to block serialized PHP objects
SecRule ARGS "@rx O:\d+:\"" "id:1001,phase:2,deny,status:403,msg:'Potential PHP Object Injection Attempt'"